George Osborne, the shadow chancellor, has sparked a bitter row by accusing Gordon Brown of adopting the principle of 'fairness' merely because of its popularity with focus groups.

He will use a speech this week to claim the Tories are now the real champions of social justice and equality, values Labour was explicitly founded to defend, and dismiss the Prime Minister's plan to relaunch his government this autumn under that banner. 'I've seen the focus groups, too. People like the word "fair". They think this government is "unfair" to those who work hard and play by the rules,' he will say in a speech to the think-tank Demos. 'And when you're in trouble, there is a temptation to cling desperately to the words that focus groups throw up.'

He will also say that the Tories are now 'the driving force behind the ideas that will create a fairer Britain'.

His words drew a furious response from Labour, which has been associated for a century with the equitable division of wealth. Treasury Minister Kitty Ussher said: 'George Osborne's claim to stand for fairness is laughable when he has committed to an inheritance tax policy which diverts £1bn to the 3,000 richest estates in the country.'